This invention relates to novel adsorbents useful in selective adsorption of unsaturated hydrocarbons manufacture of such adsorbents and process for the separation of unsaturated hydrocarbons using such adsorbents. More specifically, this invention relates to an adsorbent having a high degree of selectivity and affinity for olefin molecules and also having high adsorption capacity for olefins, and a process for producing the same. More specifically, this invention relates to ethylene and/or propylene separation process employing a specially prepared adsorbent to effectively separate ethylene and/or propylene from a gas mixture containing ethylene and/or propylene together with one or more components selected from the group consisting H2, N, Ar, He, CH4, C2H6, C3H8, CO2, and CO in an efficient manner using the adsorbent of the present invention. The adsorbents of the present invention display high adsorptive capacity for unsaturated hydrocarbons such as ethylene and propylene.
Unsaturated hydrocarbons such as ethylene, propylene and butene are basic raw materials in synthetic chemistry. These are produced by naphtha/natural gas cracking or by dehydrogenation of paraffins. Invariably, these are obtained as mixtures necessitating separation before their use. Traditionally separations of ethylene from ethane and propylene from propane have been achieved by low temperature and/or high pressure distillation. These separations are highly energy intensive and difficult to achieve. Separation of mixture of ethane-ethylene is carried out at xe2x88x9225xc2x0 C. and 320 psig in a distillation column containing over 160 trays and propane-propylene at xe2x88x9230xc2x0 C. and 30 psig pressure in a distillation column containing over 200 trays. Separations of ethane-ethylene and propane-propylene by distillation are the largest energy consuming separation processes in petrochemical industry. Furthermore, demand for ethylene and propylene is ever increasing. World wide ethylene capacity of about 100 million metric tons (mmt) per year is projected to grow to 122.1 mmt/y by 2005. For the past several years, various researchers have been working on the development of alternative technologies such as adsorption, chemical absorption and membrane separation processes. Of the various alternative technologies adsorption process appears to be the most promising. Adsorbent forms heart of any adsorption process. An adsorbent suitable for the separation of light olefin/paraffin gas mixture should have high adsorption capacity and selectivity for either olefin or paraffin. Adsorbed component should be able to desorb easily by simple chemical engineering operation such as by increasing the temperature or by reducing the pressure. Conventional adsorbents such as activated alumina, activated carbon, silica gel and zeolites known in the prior art do not show good selectivity for olefins or paraffins. Hence, development of a suitable adsorbent has become a key factor in the development of adsorption process.
The adsorbents such as ion exchanged zeolites, polymer supported silver chloride, copper-containing resins etc. known in the prior art exhibiting selectivity for ethylene or propylene suffer from one or more drawbacks such as slow adsorption kinetics, poor adsorption capacity and/or selectivity. Recently, Yang an Kikkinides (Ref, AIChE J. 41,509, 1995) and Cho and co-workers (Ind. Eng. Chem. Res., 36, 27749, 1997) have reported more promising adsorbents. Among the adsorbents reported by them, Ag+ resin and CuCl/Al2O3 showed high olefin adsorption capacity and good selectivity. However, ethylene and propylene sorption kinetic on Ag+ resin are slow. CuCl/Al2O3 is a CuCl dispersed on y-Al2O3 by monolayer dispersion technique and hence, is obtained in a powder form. For commercial use, this adsorbent needs to be shaped into pellets, which leads to reduction in adsorption capacity and selectivity. Furthermore, adsorbent formulations prepared sing Cu(I) compounds are unstable and easily get oxidized to Cu(II) leading to loss in adsorption capacity and selectivity of the adsorbent. Xie et al, (Advances in Catalysis, 1, 37, 1990) have also reported a series of adsorbents containing Cu(I). These were also prepared in powder form. Hence, these adsorbents also suffer from the above mentioned drawbacks. More recently Cho et al invented olefin selective adsorbents exhibiting superior adsorption capacity, selectivity and rates of adsorption. These were prepared by dispersing silver compound on conventional supports such as activated alumina and acid activated clay. These adsorbents possess high adsorption capacity and selectivity for olefins over paraffins compared to those reported in the prior art. However, due to ever changing business requirements and demands, it is desirable to have adsorbents exhibiting even higher adsorption capacity, selectivity and/or reversibility for efficient separation of hydrocarbon gases. The present invention now seeks to meet such demands by providing novel adsorbent formulations and methods exhibiting very high adsorption capacity, selectivity and reversibility for olefins over saturated hydrocarbons.
It is an object of the present invention to provide an adsorbent composition exhibiting high adsorption selectively and capacity for unsaturated hydrocarbons.
Yet another object of this invention is to provide a method for the production of an adsorbent possessing high adsorption capacity for selectively adsorbing unsaturated hydrocarbons.
It is yet another object of this invention is to provide improved, stable solid adsorbents) in powder, pellet or bead form for selective adsorption of saturated hydrocarbons, which adsorbent is a composite comprising (a) a silver compound or copper and (b) a suitable mesoporous substrate having a sufficiently high surface area, and highly suitable pore size distribution and which is obtainable by a process comprising dispersion/impregnation of silver compound in the support and heat treatment of the resulting composite material.
Yet another object of this invention to provide a process for the separation of ethylene, propylene and butylenes either individually or as mixture from a hydrocarbon stream containing ethylene, propylene or butylenes or mixture of together with one or more components selected from such gases as H2, N2, Ar, He, CH4, C2H6, C3H8, CO2 and CO using a mass of adsorbent.
Yet another object of this invention is to effect the above separation process at conditions of moderate temperatures (0-1 SOT) and pressures (0.1 to 100atmospheres).
It has now been found that a group of solid adsorbents in the form of powder, granules or pellets have improved adsorptive capacity, selectivity and reversibility for ethylene and/or propylene not known in the prior art and that they can be produced by a process as described below. These adsorbents comprise (a) a silver or copper compound and (b) a mesoporous substrate. These adsorbents are highly stable and are capable of reversibly adsorbing substantial quantity of ethylene and/or propylene at room temperature. The rates of adsorption of ethylene and/or propylene are also very fast in these adsorbents.
Accordingly, the present invention provides an adsorbent for selective adsorption of unsaturated hydrocarbons from its mixture with saturated hydrocarbons, carbon dioxide, carbon monoxide, permanent gases or mixture thereof comprising of:
Silver or copper compound 1 to 70 wt %
Substrate 30 to 99%
The present invention also provides a method for the manufacture of an adsorbent for use in selective adsorption of unsaturated hydrocarbons or mixtures thereof from a mixed gas, which comprises impregnating or dispersing a silver (I) or copper (I) compound on a mesoporous substrate or support to form a composite material and subjecting said composite material to heat treatment.
In another important aspect, the present invention also relates to a process for separating ethylene and/or propylene from gas mixtures containing them by passing a stream of said gas mixture through a mass of said adsorbent at a temperature from 0xc2x0 C. to 170xc2x0 C. and a pressure from 0.1 to 100 atmospheres and releasing the adsorbed ethylene and/or propylene by lowering pressure and/or increasing temperature.